FACILITIES FOR STUDY OF METAMORPHISM. 57 



south of the haiits indicated witliout .substantial change in character. The 

 stud}- is thus not one of merely local recrystallization, but of regional meta- 

 morphism, wliich is not of uniform intensity and is therefore the better 

 fitted for investigation. 



The age of the altered beds is known, from direct paleontological evi- 

 dence at a number of localities, to be Neoconiian, and there is no evidence 

 that any considerable quantity of older rocks is included witliin the area. 

 The epoch of tlie metamorphism is also clearly proved to be in the earlier 

 portion of the Cretaceous period, and probably about the close of the Neo- 

 coniian. 



The most interesting alteration processes to which the sandstones have 

 been subjected are closely similar to those whicli characterize metamorphic 

 areas elsewhere, consisting chiefly in the metasomatic' recrystallization of 

 sediments to liolocrystalline feldspathic rocks carrying feri-omagnesian sili- 

 cates and in the formation of vast quantities of serpentine. At the same 

 time these rocks present peculiarities distingui.shing them from many highly 

 altered rocks in other regions. 



The metamorphism accompanied or followed an upheaval of unusual 

 violence. Tn tlus uplift the granite must have been shattered as well as the 

 overlying strata. Tlie metamorphism was chemically of such a character 

 as to necessitate the supposition that solutions rising to the surface from the 

 shattered gnmite beneath co-operated in the process. 



Thus the origin of the sedimentary rocks, their mineralogieal cliaracter 

 in an unaltered state, their age, the approximate epocli at whicli they were 

 metamorphosed, and tlie general character of the conditious of metamor- 

 phism are all known, while the exposures illustrating the comparatively 

 few more important problems involved are numberless. I am not aware 

 that metamorphism has ever been studied under conditions so favorable for 

 elucidation. It is unnecessary' to say that the material is far from ex- 

 hausted by a single investigation. Much remains to be done, e.specially 

 from a cliemical point of view ; indeed, the chemical details of the greater 

 part of the transformations are still unknown. 



' By nietasomatism I urnierstand and desire to express a change effected by tlio action of mineral 

 solutions having an extraneous origin, but not necessarily or usually involving a total replacement of 

 the material acted upon. 



